Telephone-exchange system.



H. L. DARRAH.

TELEPHONE EXCHANGE SYSTEM,

APPLICATION FILED N0v.2l, 191s.

Patented July 10, 1917.

In venfor; Harry L. Dal rah.

TINTTED %TATES PATENT @FETQE.

HARRY L. DARRAH, OF CHATHAIVI, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed November 21, 1916.

To all whom it may concern:

Be it known that I, HARRY L. DARRAII, a citizen of the United States, residing at Chatham, in the county of Morris and State of New Jersey, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems and more particularly to private branch exchange systems.

The present invention is an improvement upon the system disclosed in the Patent No. 1,175,112 to H. M. Bascom, and concerns organizations of circuits and apparatus therefor for increasing the transmission ef ficiency of such systems and the provision of improved signaling means between the central ofiice and private branch exchange operators.

This invention is illustrated in the accompanying drawing in which a trunk circuit A extends from a central office at which is located a link circuit B, and a private branch exchange at which is located a cord circuit C for interconnecting extension telephone lines D or for connecting trunk circuit A with an extension telephone line D.

Assuming that the operator at the central ofiice has been requested to make connection with an extension line which terminates at the private branch exchange, the operator will insert plug 5 of the link circuit B into the jack 6 of trunk circuit A, whereupon relay 7 located at the private branch exchange and associated with the end of the trunk circuit A terminating thereat, will be operated by current from a source of supply 8. Relay 7 in operating, completes a locking circuit for itself through its right-hand winding and through its contact, whereby lamp 9 is lighted over a circuit from battery through the lower right-hand contact of key 10, winding of relay 11, lamp 9, lower contact of jack 12, and contact of relay 7 to ground. The operation of relay 11 causes the operation of an alternating current buzzer 13, which serves as an audible signal to the operator at the private branch exchange.

The operator at the private branch exchange, hearing the buzzer and observing the lighted condition of lamp 9, inserts front plug 15 of the cord circuit G into jack 12, thereby opening the circuit of lamp 9 and Specification of Letters Patent.

Patented July 10, 1917.

Serial No. 132,560.

the locking circuit of relay 7, and causing the operation of relay 16 over a circuit from battery through the lower right-hand con tact olt key 10, resistance 17, sleeve contacts of the jack .12 and plug 15 and the winding of relay 16 to ground. The operation of relay 16 causes the operation of relay 30 which in closing its contact 29 short circuits supervisory relay 31, and in closing its upper alternate contact causes lamp 32 to be lighted. The operation of relay 16 also disconnects the battery supply from, and bridges impedance coils 18 and 19 in series across, the talking strands of the cord circuit C. The impedance of these two coils is low so that tripping relay 20, associated with link circuit B, operates, whereupon relay 21 operates, locks up and permits the release of relay 22. Supervisory relay 23 is thereupon operated over a circuit from battery in the link circuit B, through the upper winding of repeating coil, winding of supervisory relay 23, upper normal contact of relay 22, tip contacts of the plug 5 and jack 6, tip contacts of the jack 12 and plug 15, contact 24 of key 25, impedance coil 19, contact 26 of relay 16, contact 27 of relay 28, impedance coil 18, contact 29 of relay 30, contact 35 of key 25, ring contacts of plug 15 and jack 12, ring contacts of jack 6 and plug 5, lower normal contact of relay 22 and the lower winding of the repeating coil to ground. The operation of the supervisory relay 23 eiiaces lamp 36 which had been lighted when the plug 5was inserted in the jack 6, the efl'acing of this lamp indicating to the central oliice operator that the private branch exchange operator has answered.

The private branch exchange operator may now actuate listening-key 4:0 to connect operators telephone set 41 across the talking strands of cord circuit C. The actuation of key 10 closes a circuit for battery supply through relay 4:2 and an impedance coil 13 to the transmitter of the operators telephone set, and in addition thereto, causes the operation of relay 33 over a circuit from battery through contact 44 of relay 16, lefthand winding of relay 33, resistance 45 and contact 46 to ground. The operation of relay 33 connects its right-hand winding in parallel with impedance coil 18, thereby serving to lock up relay 33, the source of current supply therefor being the battery across the talking strands in the link circuit B. The connection of the right-hand winding of relay 33 in parallel with impedance coil 18 slightly lowers the impedance of the bridge. The operation of relay 33 also opens its right-hand normal contact, thereby efiiacing the lamp 32, which was lighted when plug 15 was inserted in jack 12.

The private branch exchange operator being informed that connection is desired with extension line D, inserts the back plug 47 in jack 48 associated with line D, whereupon lamp 49 is lighted over a circuit from battery through the upper right-hand contact of key 10, winding of relay 50, lamp 49, normal contact of supervisory relay 51., sleeve contacts of plug L? and jack 4:8 to ground. If the operator has restored listening-key 40 to normal position, relay 4L2 will be in its normal position, whereby, upon the operation of relay 50, buzzer 13 operates. However, the operation of buzzer 13 at this time serves no useful purpose, so that the operator may actuate key 10 to open its left-hand contacts to stop the operation of the buzzer. The operator may signal the station on line D by the operation of the usual ringing key 52. v

The subscriber at the station on line D, responding to the operation of the call bell, causes the operation oi the supervisory relay 51, relay 51. being placed in series with thetransmitter and switchhook contact of station D, which is now in parallel with the impedance bridge across the talking strands of the cord circuit C. The operation of supervisory relay 51 eiiaces lamp a9 and causes the operation of relay 28 over a circuit from battery through contact at of relay 16, lefthand winding of relay 38, winding of relay 28, alternate contact of relay 51, and sleeve contacts of plug 4-7 and jack 18 to ground. llelay 29, in operating, opens its contacts 27 and 53 and closes its contact 54, thereby changing the impedance bridge across the talking strands of the cord circuit from a low impedance bridge including impedance coils 18 and 19 in series with the right-hand winding of relay 33 bridged about impedance coil 18, to a high impedance bridge including the impedance coil 19, right-hand winding of relay impedance coil and impedance coil 18 in series. This bridge is changed from low to high impedance so that it the extension subscriber should desire to attract the attention of the private branch exchange operator by opening and closing the switchhook contact, this may be done without affecting the condition of the lamp 36 associated with the link circuit B.

At the conclusion of the conversation be tween extension subscriber D and the subscriber connected to the other end of link circuit B, the restoration of the receiver to the switchhook by extension subscriber D causes the release of relay 51 and the lightscriber, responding,

ing of lamp 49 to furnish a disconnect signal. Relay 28 also releases, changing the bridge across the talking strands of the cord circuit from high to low impedance. The private branch exchange operator now with draws the plugs from the acks, whereupon supervisory relay 23 releases to light the lamp 36 to furnish a disconnect signal to the central oflice operator, who may now with draw plug 5 from jack 6, thereby restoring all apparatus to normal.

Suppose that, after the listeningkey 4L0 has been restored to normal, the central office operator wishes to reringor again signal the operator at the private branch exchange. This may be done by withdrawing the plug 5 from and reinserting the plug 5 in the jack 6. Upon the withdrawal of plug 5 from jack 6, the circuit through the locking-winding of relay 33 is opened, thereby releasing this relay, causing lamp 32 to light. The reinsertion of the plug in the jack 6 does not reestablish the circuit throughthe right-hand winding of relay 33 since this relay can only be energized by the actuation of listening-key 4-0. The private branch exchange operator, noting the lighted condi tion of lamp 32, responds by actuating the listening-key, causing the operation and locking up of relay 33, as before described.

Should the subscriber on extension line D initiate a call, the removal of the receiver from the switchhook causes line lamp 60 to light and also causes the operation of relay- 11, whereupon buzzer 13 operates. The operator responds by inserting plug l7 into jack 48, thereby effacing line lamp 60, and causing the operation of supervisory relay 51 to prevent the lighting of lamp 49. Nhen plug 47 is inserted in jack 4L8, lamp 332 is lighted over. a circuit from battery through lamp 32, normal contact of relay '30,

normal contact of relay 31, and sleeve con tacts of plug l7 and jack &8 to ground; The operator may actuate listeningrkey 4:0 and converse with the subscriber. Upon being advisedthat subscriber D wishes to be connected with another extension line, the operator restores listening-key L0 to normal. position and inserts plug 15 into the jack of another extension line. It will be noted that relay 16 does not operate, for the sleeves of the jacks associated with the extension lines are grounded while the jack associated with the trunk is connected withbattery, so that talking battery is supplied .to the talking strands of cord circuit (1 through the normal contacts of relay 16. The operator may signalon the wanted extension line by operating ringing key 61. The called subremoves the receiver from the switchhook and causes the operation of. supervisory relay 31, thereby efiaction with a line terminating at the central office, the operator would have inserted plug into jack 12 of the trunk A, thereby causing the operation of relay 16 to remove battcry supply from cord circuit C to bridge the impedance coils 18 and 19 in series across the talking strands and to cause the operation of relay to short-circuit supervisory relay 31 and place lamp 82 under control of relay 33. The establishment of the bridge across the talking strands of the cord circuit causes the operation of line relay at the central oflice end of the trunk, thereby causing the operation of the line lamp (3G. The central ol'iice operator, responding, inserts the plug 5 of the link circuit B into jack 6, thereby operating the cut-off relay associated with the trunk. The private branch exchange operator may now actuate listening-key 40 and converse with the operator at the central ofice. The actuation of listening-key 40 causes the operation of relay 33, as hereinbefore described.

If it is desired that extension line D be connected by means of the cord circuit C to the trunk A to be able to receive service dur ing the night or when no operator is at the private branch exchange, this may be done by actuating key 25 and key 10 to open its right-hand contacts and by inserting plug 15 into jack 12 of the trunk circuit A and plug d7 into jack A8 of extension line 48. The actuation of key 25 by opening its normal contacts removes all apparatus from the talking strands of the cord circuit, and by closing its alternate contacts, extends the trunk line A through to extension line D. The actuation of key 10 in opening its right-hand contacts removes battery from the lamps associated with the cord circuit.

C and from the sleeve of the trunk circuit thereby preventing the operation of relay 16.

By employing the invention hereinbefore described, the source of ringing current is automatically disconnected from the trunk circuit immediately upon the connection of the private branch exchange cord circuit with the trunk circuit, it being very desirable that this source be disconnected before the operators telephone set is connected with the cord circuit. This invention also provides for the reringing of the private branch exchange operator by the central office operator without the lighting of the supervisory lamp in the central office link circuit which has been a source of confusion of signals in systems heretofore employed.

What is claimed is:

1. A telephone exchange system comprising calling and called telephone lines, a link circuit for connecting the lines, a relay responsive to the connection of the link circuit with the calling line, a bridge forthe talking strands of the link circuit established upon the operation of the relay, and means for increasing the impedance of the bridge upon the removal from its switchhook of the receiver at the station on the called. line connected with the other end of the link circuit.

2. A telephone exchange system comprising calling and called telephone lines, a link circuit for connecting the lines, a relay responsive to the connection of the link circuit with the calling line, a low impedance bridge for the talking strands of the link circuit established upon the operation. of the relay, and a relay for varying the impedance of the bridge upon the removal from its switchhook of the receiver at the station on the called line connected with the other end of the link circuit.

3. A telephone exchange system comprising calling and called telephone lines, a link circuit for connecting the lines, a relay responsive to the connection of the link circuit with the calling line, a bridge for the talking strands of the link circuit established upon the operation of the relay, a relay for increasing the impedance of the bridge, and a circuit for the last mentioned relay controlled from the station on the called line connected with the other end of the link circuit.

4. A telephone exchange system comprising calling and called telephone lines, a link circuit for connecting the lines, a relay responsive to the connection of the link circuit with the calling line, a bridge for the talking strands of the link circuit established upon the operation of the relay, an operators telephone set, means actuated to connect the telephone set to the link circuit, a relay responsive to the actuation of the means to connect a winding thereof in parallel with a portion of the bridge, and a sig naling device controlled by the last mentioned relay.

5. A telephone exchange system comprising calling and called telephone lines, a link circuit for connecting the lines, a relay responsive to the connection of the link circuit with the calling line, a bridge for the talking strands of the link circuit established upon the operation of the relay, an operators telephone set, a listening key for connecting the operators telephone set to the link circuit, a relay responsive to the actuation of the listening-key to connect a winding thereof in parallel with a portion of the bridge, and a signaling device controlled by the last mentioned relay.

6. A telephone exchange system comprising calling and called telephone lines, a link circuit for connecting the lines, a. relay responsive to the connection of the link circuit with the calling line, a low impedance bridge for the talking strands of the link circuit established upon the operation of the relay, an operators telephone set, a

listening-key for connecting the operatofs telephone set to the link circuit, a relay responsive to the actuation of the listening-key to connect a Winding thereof in said bridge and to lock up the last mentioned relay, a signaling device, and an operating circuit for the signaling device completed by the release of the last mentioned relay upon the opening of the calling line.

7 A telephone exchange system comprising calling and called telephone lines, a link circuit for connecting the lines, a relay responsive to the connection of the link circuit with the calling line, a low impedance bridge for the talking strands of the link circuit established upon the operation of the relay, an operators telephone set, a listening-key for connecting the operators telephone set to the link circuit, a relay responsive to the actuation of the listening-key to tact of the second mentioned relay.

In Witness whereof, I hereunto subscribe my name thls 20th day of November A. 1).,

HARRY L. DARRAH.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. C. 

